Method of making a magnetoresistive element

ABSTRACT

A method of making a magnetoresistive element comprises making a crystalline structural quality and magnetic anisotropy enhancement bilayer (CSMAE bilayer) thus a). enhancing the crystalline structural quality, hence fabrication yield, of the resulting magnetoresistive element; and b). enhancing the magnetic anisotropy of the recording layer whereby achieving a high MR ratio for the magnetoresistive element with a simultaneous reduction of an undesirable spin pumping effect. As the magnetoresistive film is thermally annealed, a crystallization process occurs to form bcc CoFe grains having epitaxial growth with (100) plane parallel to the surface of the tunnel barrier layer as Boron elements migrate into the impurity absorbing layer. Removing the top portion of the impurity absorbing layer by means of sputtering etch or RIE etch processes followed by optional oxidization process, a thin but thermally stable portion of impurity absorbing layer is formed on top of the magnetoresistive element with a low damping constant. Accordingly, a reduced write current can be achieved for spin-transfer torque MRAM application.

RELATED APPLICATIONS

This application is a divisional application due to a restrictionrequirement on application Ser. No. 14/073,844. This application seekspriority to U.S. Utility patent application Ser. No. 14/073,844 filed onNov. 6, 2013 and U.S. Provisional Patent Application No. 61/745,757,filed on Dec. 24, 2012; the entire contents of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of magnetoresistive elements. Morespecifically, the invention comprises spin-transfer-torquemagnetic-random-access memory (MRAM) using magnetoresistive elements asbasic memory cells which potentially replace the conventionalsemiconductor memory used in electronic chips, especially mobile chipsfor power saving and non-volatility.

2. Description of the Related Art

In recent years, magnetic random access memories (hereinafter referredto as MRAMs) using the magnetoresistive effect of ferromagnetic tunneljunctions (also called MTJs) have been drawing increasing attention asthe next-generation solid-state nonvolatile memories that can cope withhigh-speed reading and writing, large capacities, andlow-power-consumption operations. A ferromagnetic tunnel junction has athree-layer stack structure formed by stacking a recording layer havinga changeable magnetization direction, an insulating spacing layer, and afixed reference layer that is located on the opposite side from therecording layer and maintains a predetermined magnetization direction.

As a write method to be used in such magnetoresistive elements, therehas been suggested a write method (spin torque transfer switchingtechnique) using spin momentum transfers. According to this method, themagnetization direction of a recording layer is reversed by applying aspin-polarized current to the magnetoresistive element. Furthermore, asthe volume of the magnetic layer forming the recording layer is smaller,the injected spin-polarized current to write or switch can be alsosmaller. Accordingly, this method is expected to be a write method thatcan achieve both device miniaturization and lower currents.

Further, as in a so-called perpendicular MTJ element (equivalentlyreferred to as the “magnetoresistive element”), both two magnetizationfilms have easy axis of magnetization in a direction perpendicular tothe film plane due to their strong magnetic crystalline anisotropy(shape anisotropies are not used), and accordingly, the device shape canbe made smaller than that of an in-plane magnetization type. Also,variance in the easy axis of magnetization can be made smaller.Accordingly, by using a material having a large perpendicular magneticcrystalline anisotropy, both miniaturization and lower currents can beexpected to be achieved while a thermal disturbance resistance ismaintained.

There has been a known technique for achieving a high MR ratio in aperpendicular MTJ element by forming an underneath MgO tunnel barrierlayer and a bcc or hcp-phase cap layer that sandwich a thin recodinglayer having an amorphous CoFeB ferromagnetic film and acceleratecrystallization of the amorphous ferromagnetic film to match interfacialgrain structure to MgO layer through a thermal annealing process. Therecording layer crystallization starts from the tunnel barrier layerside to the cap layer and forms a CoFe grain structure having aperpendicular magnetic anisotropy, as Boron elements migrate into thecap layer. Accordingly, a coherent perpendicular magnetic tunnelingjunction structure is formed. By using this technique, a high MR ratiocan be achieved.

However, where a cap layer is used for achieving a high MR ratio in anMTJ element, the cap layer may increase the damping constant of therecording layer, due to the so-called spin-pumping effect. Further, thedamping constant of the recording layer may also increase from theadditional cap layer material diffusion during the heat treatment in thedevice manufacturing process.

In a spin-injection MRAM using either a perpendicular or planarmagnetization film, a write current is proportional to the dampingconstant and inversely proportional to a spin polarization. Therefore,reduction of the damping constant and increase of the spin polarizationare mandatory technologies to reduce the write current.

BRIEF SUMMARY OF THE PRESENT INVENTION

Present invention illustrates a method of making one or moreperpendicular magnetoresistive elements for perpendicularspin-transfer-torque MRAM with improved quality and yield.

The method presented in present invention makes a perpendicularmagnetoresistive element to be sandwiched between an upper electrode anda lower electrode of each MRAM memory cell, together with a writecircuit which bi-directionally supplies a spin polarized current to themagnetoresistive element and a select transistor electrically connectedbetween the magnetoresistive element and the write circuit.

The method of making such a perpendicular magnetoresistive elementcomprises: forming a reference layer having magnetic anisotropy in adirection perpendicular to a film surface of the reference layer andhaving an invariable magnetization direction; forming a tunnel barrierlayer on the reference layer; forming a recording layer having magneticanisotropy in a direction perpendicular to a film surface of thereference layer and having a variable magnetization direction on thetunnel barrier layer; and forming a “crystalline structural quality andmagnetic anisotropy enhancement bilayer” (CSMAE bilayer) comprising arecording layer and a novel impurity absorbing layer with one or moreimpurity absorbing sub-layer(s) atop the recording layer. Such animpurity absorbing layer with one or more impurity absorbingsub-layer(s) may be hereafter simply, equivalently, or interchangeablynamed as a cap layer or a cap multilayer with one or more sub-layer(s).Then device in process is treated with a thermal annealing process. Akey technique in present invention is removing at least the top portionor upper portion of the cap layer or cap multilayer (i.e. a sacrificiallayer) after conducting a thermal annealing process on themagnetoresistive film but keeping the remaining portion of the cap layeratop the recording layer with a reasonable thickness that has anincreased thermal stability due to annealing, whereby damping constantof the recording layer, due to the so-called spin-pumping effect, isreduced by this process of trimming the top portion of the cap layerthat has absorbed significant amount of impurity Boron migrated from therecording layer.

As an amorphous ferromagnetic material, like CoFeB, in the recordinglayer is thermally annealed, a crystallization process occurs to formbcc CoFe grains having epitaxial growth with (100) plane parallel to thesurface of the tunnel barrier layer to form a perpendicular anisotropyas Boron elements migrate into the impurity absorbing layer, i.e., caplayer or cap multilayer. In this case, the “impurity” element inside therecording layer is Boron. Removing the top portion of the cap layer bymeans of sputtering etching including ion bean etching (IBE) or reactiveion etching (RIE) process(es), followed by an oxidization process whennecessary, a thin but thermally stable portion of the cap layer ispreserved atop the recording layer. Thus a recording layer having alower damping constant and requiring a reduced write current for writingis achieved.

The method illustrated in present invention is also suitable for makingplanar magnetoresistive elements also known as parallel (parallel to afilm surface of the reference layer), spin-transfer-torque MRAM.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view showing a configuration of an MTJelement 10 as deposited, according to the method illustrated in firstembodiment;

FIG. 1B is a cross-sectional view showing a configuration of an MTJelement 10 after IBE etching process to remove the protective layer andtop portion of the impurity absorbing layer, according to the methodillustrated in first embodiment;

FIG. 2 is a cross-sectional view showing a configuration of an MTJelement 10 after an optional top surface oxidization of the remainingimpurity absorbing layer, followed by deposition of a upper-contactmultilayer film comprising a buffer layer and a photoresist layer;

FIG. 3A is a cross-sectional view showing a configuration of an MTJelement 10 as deposited, according to the method illustrated in secondembodiment;

FIG. 3B is a cross-sectional view showing a configuration of an MTJelement 10 after the 1^(st) RIE or IBE etching process to remove theprotective layer, according to the method illustrated in secondembodiment;

FIG. 3C is a cross-sectional view showing a configuration of an MTJelement 10 after the 2^(nd) RIE etching process to remove the second capsub-layer (equivalently referred to as the “second impurity absorbingsub-layer”), according to the method illustrated in second embodiment;

FIG. 4A is a cross-sectional view showing a configuration of an MTJelement 10 as deposited, according to the method illustrated in thirdembodiment;

FIG. 4B is a cross-sectional view showing a configuration of an MTJelement 10 after the 1^(st) RIE or IBE etching process to remove theprotective layer and the third cap sub-layer (equivalently referred toas the “third impurity absorbing sub-layer”), according to the methodillustrated in third embodiment;

FIG. 4C is a cross-sectional view showing a configuration of an MTJelement 10 after the 2^(nd) RIE etching process to remove the secondimpurity absorbing sub-layer, according to the method illustrated inthird embodiment;

FIG. 5 is a cross-sectional view showing a configuration of an MTJelement 10 as deposited, according to the method illustrated in fourthembodiment;

FIG. 6 is a cross-sectional view showing a configuration of an MTJelement 10 after an optional top surface oxidization of the remainingfirst impurity absorbing sub-layer”, followed by deposition of aupper-contact layer film comprising a buffer layer and a photoresistlayer, according to the method illustrated in fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In general, according to one embodiment in present invention, making amagnetoresistive element comprising:

forming a reference layer having magnetic anisotropy and having aninvariable magnetization direction;

forming a tunnel barrier layer atop the reference layer;

forming a recording layer atop the tunnel barrier layer and having avariable magnetization direction;

forming an impurity absorbing layer, with one or more impuritysublayer(s), i.e., a cap layer or cap multilayer, atop the recordinglayer;

forming a protective layer atop the cap multilayer, wherein theprotective layer and at least the top portion of the cap layer or capmultilayer are later removed or trimmed after conducting a thermalannealing process on the magnetoresistive film but keeping the remainingportion of the cap layer, interfacing the recording layer, with areasonable thickness that has an increased thermal stability due toannealing;

employing an oxidization process to oxidize the top surface of theremaining cap layer when necessary; and

forming an upper-contact layer provided on the remaining cap layer,comprising a buffer layer and a photoresist layer for furtherphoto-lithographic processes of making a magnetoresistive element.

First Embodiment

FIG. 1A and FIG. 1B are cross-sectional views showing a configuration ofan MTJ element 10 as deposited according to the method described infirst embodiment. The MTJ element 10 is configured by stacking a bottomelectrode 11, a base layer (equivalently referred to as the “seedlayer”) 12, a reference layer 13, a tunnel barrier layer 14, a recordinglayer 15, a cap layer 16, and a protective layer 17 in this order fromthe bottom.

The reference layer 13 and the recording layer 15 are made of aferromagnetic material, and have uni-axial magnetic anisotropy in adirection perpendicular to the film surfaces. Further, directions ofeasy magnetization of the reference layer 13 and the recording layer 15are also perpendicular to the film surfaces. In other words, the MTJelement 10 is a perpendicular MTJ element in which magnetizationdirection of the reference layer 13 and the recording layer 15 faces ina direction perpendicular to the film surfaces. A direction of easymagnetization is a direction in which the internal magnetic energy is atits minimum where no external magnetic field exists. Meanwhile, adirection of hard magnetization is a direction in which the internalenergy is at its maximum where no external magnetic field exists.

The recording layer 15 has a variable (reversible) magnetizationdirection. The reference layer 13 has an invariable (fixing)magnetization direction. The reference layer 13 is made of aferromagnetic material having a perpendicular magnetic anisotropicenergy which is sufficiently greater than the recording layer 15. Thisstrong perpendicular magnetic anisotropy can be achieved by selecting amaterial, configuration and a film thickness. In this manner, a spinpolarized current may only reverse the magnetization direction of therecording layer 15 while the magnetization direction of the referencelayer 13 remains unchanged. An MTJ element 10 which comprises arecording layer 15 having a variable magnetization direction and areference layer 13 having an invariable magnetization direction for apredetermined write current can be achieved.

The tunnel barrier layer 14 is made of a non-magnetic insulating metaloxide or nitride.

The cap layer 16 is made of a low electro-negativity and low diffusivitymetal layer or a metal alloy layer having a bcc or hcp-phase and havingat least a thickness of 50 angstroms. The cap layer serves to introduceand to enhance crystalline structural quality and perpendicular magneticanisotropy of the recording layer 15. As an amorphous ferromagneticmaterial, like CoFeB, in the recording layer is thermally annealed, acrystallization process occurs to form bcc CoFe grains having epitaxialgrowth with (100) plane parallel to surface of the tunnel barrier layerand a perpendicular anisotropy is induced in the recording layer, asBoron elements migrate into the cap layer having a lowelectro-negativity. A damping constant of the recording layer 15sometimes increases (deteriorates) depending on a material in contactwith the recording layer 15, which is known as a spin pumping effect.The cap layer 16 may also have a function to prevent increase of thedamping constant of the recording layer 15 by reducing the spin pumping.Further, the thickness of the cap layer 16 is selected to be big enoughthat it serves as a good absorber for the Boron elements from therecording layer to achieve better epitaxial CoFe crystal grains in therecoding layer having an ultra-low damping constant.

An example configuration of the MTJ element 10 will be described below.The reference layer 13 is made of CoFeB (around 2 nm)/TbCoFe (around 20nm). The tunnel barrier layer 14 is made of MgO (around 1 nm). Therecording layer 15 is made of CoFeB (around 1.2 nm). The cap layer 16 ismade of Ti (around 10 nm). The protective layer 17 is made of Ru (around10 nm). The base layer 12 is made of Ta (around 20 nm)/Cu (around 20nm)/Ta (around 20 nm). Each element written in the left side of “/” isstacked above an element written in the right side thereof.

The CoFeB (with Boron content no less than 10% and no more than 30%)layer comprised in the recording layer 15 is in an amorphous state asdeposited. The MgO layer comprised in the tunnel barrier layer 14 isformed into rocksalt crystal grains with the (100) plane parallel to thesubstrate plane. During a thermal annealing with a temperature higherthan 250-degree C, the Boron elements of the CoFeB migrate into itsabove Ti cap layer to form TiB2 since Ti has much lowerelectro-negativity than Co and Fe, and the amorphous CoFeB iscrystallized to form bcc CoFe grains having epitaxial growth with (100)plane parallel to the surface of the MgO crystal tunnel barrier layer. Athick Ti cap layer is essential to absorb as many as Boron atoms aspossible and achieve better epitaxial bcc CoFe crystal grains. Arelatively pure CoFe film has a lower damping constant than an amorphousCoFeB film. A typical damping constant for a pure CoFe is around 0.003,while CoFeB has a damping constant of 0.01. Accordingly, a perpendicularmagnetization having a low damping constant is induced in the recordinglayer.

After the thermal annealing process, an IBE etching process is adoptedto etch away the Ru protective layer and the top portion of the Ti caplayer, leaving a much thinner remaining Ti cap layer for an easyintegration with very small dimension lithographic patterning process,as shown in FIG. 1B. An upper contact layer 19 (not shown) comprising abuffer layer and a photoresist layer is then deposited on the top of MTJfilm after the etching.

Then, if necessary, a surface oxidization process may also be addedbefore the upper contact layer deposition. A surface oxidizationprocess, i.e. by using of a mixed gas containing natural oxygen (O₂), orradical oxygen and Argon (Ar), may also be adopted before the depositionof the upper contact layer. Doing so, a thin oxide layer 16B is formedbetween the remaining cap layer 16A and the upper contact layer 20 forbetter interfacial thermal stability and less diffusion. The finalconfiguration of the MTJ element 10, which is ready for MTJ elementphotolithographic patterning process, is shown in FIG. 2.

Second Embodiment

FIG. 3A is a cross-sectional view showing an example configuration ofthe MTJ element 10 as deposited according to the method described insecond embodiment. As shown in FIG. 3A, the reference layer 13 is madeof CoFeB (around 2 nm)/TbCoFe (around 20 nm). The tunnel barrier layer14 is made of MgO (around 1 nm). The recording layer 15 is made of CoFeB(around 1.2 nm). The first cap sub-layer (equivalently referred to asthe “first impurity absorbing sub-layer”) 16 is made of Ti (around 2nm). The second cap sub-layer (equivalently referred to as the “secondimpurity absorbing sub-layer”) 17 is made of Ta (around 10 nm). Theprotective layer 18 is made of Ru (around 10 nm). The base layer is madeof Ta (around 20 nm)/Cu (around 20 nm)/Ta (around 20 nm). Each elementwritten in the left side of “/” is stacked above an element written inthe right side thereof.

Similar to the first embodiment, the CoFeB (with Boron content no lessthan 10% and no more than 30%) layer comprised in the recording layer 15is formed into an amorphous state as deposited. During a thermalannealing with a temperature higher than 250-degree, the Boron elementsof the CoFeB migrate first into its above thin Ti cap sub-layer 16 andfurther across Ti cap sub-layer into the Ta cap sub-layer 17, since Taatom has a even lower electro-negativity and a stronger Boron-bondingthan Ti atom. The ionicity of metal-Boron bonds decreases in thefollowing order: Mg, Al, Mn, Y, Cr, Zr, Hf, Nb, Ta, V and Ti.Accordingly, the amorphous CoFeB in the recording layer is crystallizedto form bcc CoFe grains having epitaxial growth with (100) planeparallel to surface of the MgO crystal tunnel barrier layer, and aperpendicular magnetization having a low damping constant is induced inthe recording layer.

After the thermal annealing process, a RIE etching process utilizingCH3OH gas, or NH3+CO mixed gas chemistry can be employed to etch awaythe protective Ru layer 18 and the second cap Ta sub-layer serves as itsetch-stop layer, as shown in FIG. 3B. Alternatively, an IBE etchingprocess is utilized to etch away the protective Ru layer 18 and theupper portion of the second cap Ta sub-layer 17. The remaining Ta capsub-layer is readily removed by the 2^(nd) RIE etching process utilizingCF4 gas chemistry, leaving a thin Ti first cap sub-layer, as shown inFIG. 3C, for an easy integration with very small dimension lithographicpatterning process. Following an optional surface oxidization process ifnecessary, also similar to the first embodiment, an upper contact layer20 comprising a buffer layer and a photoresist layer is then depositedon the top of MTJ film, and the final configuration of the MTJ element10, which is ready for MTJ element photolithographic patterning process,is shown in FIG. 2.

Third Embodiment

FIG. 3A is a cross-sectional view showing an example configuration ofthe MTJ element 10 as deposited according to the method described insecond embodiment. As shown in FIG. 3A, the reference layer 13 is madeof CoFeB (around 2 nm)/TbCoFe (around 20 nm). The tunnel barrier layer14 is made of MgO (around 1 nm). The recording layer 15 is made of CoFeB(around 1.2 nm). The first cap sub-layer (equivalently referred to asthe “first impurity absorbing sub-layer”) 16 is made of Ti (around 2nm). The second cap sub-layer (equivalently referred to as the “secondimpurity absorbing sub-layer”) 17 is made of Ta (around 10 nm). Theprotective layer 18 is made of Ru (around 10 nm). The base layer is madeof Ta (around 20 nm)/Cu (around 20 nm)/Ta (around 20 nm). Each elementwritten in the left side of “/” is stacked above an element written inthe right side thereof.

Similar to the first and second embodiments, the CoFeB (with Boroncontent no less than 10% and no more than 30%) layer comprised in therecording layer 15 is formed into an amorphous state as deposited.During a thermal annealing with a temperature higher than 250-degree,the Boron elements of the CoFeB migrate first into its above thin Ti capsub-layer 16 and thin Ta cap sub-layer 17, and further across them intothe Hf cap sub-layer 18, since Hf atom has a even lowerelectro-negativity and a stronger Boron-bond than both of Ti atom and Taatom. From the first cap sub-layer to the third cap sub-layer, the bondiconicity with Boron atom gradually increases and more effectivelyattracts or absorbs Boron elements from the CoFeB recording layer.Accordingly, the amorphous CoFeB in the recording layer is crystallizedto form better bcc CoFe grains having epitaxial growth with (100) planeparallel to surface of the MgO crystal tunnel barrier layer, and aperpendicular magnetization having a low damping constant is induced inthe recording layer.

After the thermal annealing process, the 1^(st) RIE etching processusing CH3OH gas, or NH3+Co mixed gas chemistry is employed to etch awaythe protective Ru layer 19 and the third cap Hf sub-layer 18, stoppingat Ta cap sub-layer 17, as shown in FIG. 4B. The remaining Ta capsub-layer is then readily removed by the 2^(nd) RIE etching processusing CF4 gas chemistry, leaving a thin Ti first cap sub-layer, as shownin FIG. 4C, for an easy integration with very small dimensionlithographic patterning process. Following an optional surfaceoxidization process, also similar to the first embodiment, an uppercontact layer 20 comprising a buffer layer and a photoresist layer isthen deposited on the top of MTJ film, and the final configuration ofthe MTJ element 10, which is ready for MTJ element photolithographicpatterning process, is shown in FIG. 2.

Fourth Embodiment

Similar to above embodiments, the same cap multilayer can be adopted ina planar magnetoresistive element. FIG. 5 is a cross-sectional viewshowing an example configuration of the MTJ element 10 according to themethod described in fourth embodiment. All layered configuration can beidentical to those of the third embodiment, except that the referencelayer has an invariable magnetization in a direction parallel to a filmsurface and the recording layer has a variable magnetization in adirection parallel to a film surface. After the same thermal annealingand etching processes are utilized, the final configuration of the MTJelement 10, which is ready for MTJ element photolithographic patterningprocess, is shown in FIG. 6.

While certain embodiments have been described above, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions. Indeed, the novel embodimentsdescribed herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe embodiments described herein may be made without departing from thespirit of the inventions. The accompanying claims and their equivalentsare intended to cover such forms or modifications as would fall withinthe scope and spirit of the inventions.

The invention claimed is:
 1. A method of fabricating a magnetoresistiveelement comprises: providing a seed layer; forming a reference layer,atop the seed layer, having a magnetic anisotropy with an invariablemagnetization direction; forming a tunnel barrier layer atop thereference layer; forming, atop the tunnel barrier layer, a crystallinestructural quality and magnetic anisotropy enhancement bilayer (CSMAEbilayer) comprising an impurity absorbing layer with an interimthickness; annealing the CSMAE bilayer for crystalline structuralquality and magnetic anisotropy enhancement; and etching out a topportion of the device in process until the impurity absorbing layer isreduced to a desirable thickness, whereby an undesirable spin pumpingeffect associated with the interim thickness of the impurity absorbinglayer is mitigated.
 2. The method of claim 1 wherein forming the CSMAEbilayer comprises 2a) forming the recording layer comprising: 2a1) anumber of ferromagnetic elements necessary for forming a magneticanisotropy therein, ideally made by materials comprising Cobalt andIron; plus 2a2) a number of crystalline structural quality enhancement(CSQE) elements necessary for forming the recording layer for achievingimproved yield; 2b) forming the impurity absorbing layer with ability toabsorb, while under an annealing environment, the CSQE elements migratedfrom the recording layer, whereby: 2b1) enhancing the crystallinestructural quality, hence fabrication yield, of a resultingmagnetoresistive element; and 2b2) enhancing the magnetic anisotropy ofthe recording layer whereby achieving a high MR ratio for themagnetoresistive element with a simultaneous reduction of an undesirablespin pumping effect.
 3. The method of claim 2 wherein the CSQE elementscomprises Boron, in form(s) including but not limited to one or more ofCoFeB and a mixture of CoB and FeB, ideally with a ratio of Boron over arecording layer compound between 10% and 30%.
 4. The method of claim 2wherein the recording layer comprises one or more of recordingsub-layers.
 5. The method of claim 1 wherein the impurity absorbinglayer comprises one or more impurity absorbing sub-layers with a firstimpurity absorbing sub-layer located atop the recording layer and eachsubsequent impurity absorbing sub-layer located atop its precedingimpurity absorbing sub-layer.
 6. The method of claim 5 wherein eachsubsequent impurity absorbing sub-layer comprises a metal havingstronger bond iconicity with CSQE elements than the preceding impurityabsorbing sub-layer.
 7. The method of claim 5 wherein each impurityabsorbing sub-layers comprises metals selected from a group consistingof: Ti, V, Ta, Nb, Hf, Zr, W, Mo, Cr, Mg, and Al.
 8. The method of claim5 wherein, after forming the impurity absorbing sub-layers, the interimthickness of each impurity absorbing sub-layer is in a range from about10 Angstroms to about 100 Angstroms.
 9. The method of claim 5 whereinforming the impurity absorbing sub-layers comprises: forming a firstimpurity absorbing sub-layer composed of Titanium atop the recordinglayer; and forming a second impurity absorbing sub-layer composed ofTantalum atop the first impurity absorbing sub-layer.
 10. The method ofclaim 5 wherein forming the impurity absorbing sub-layers alternativelycomprises: forming a first impurity absorbing sub-layer composed ofTitanium atop the recording layer; forming a second impurity absorbingsub-layer composed of Tantalum atop the first impurity absorbingsub-layer; and forming a third impurity absorbing sub-layer composed ofHafnium atop the second impurity absorbing sub-layer.
 11. The method ofclaim 1 wherein the tunnel barrier layer comprises at least one memberof nonmagnetic metal oxide consisting of: MgO, ZnO, and MgZnO.
 12. Themethod of claim 1 wherein annealing the CSMAE bilayer comprising aheating process at a temperature higher than 250 degrees Celsius. 13.The method of claim 1 further comprises, between the steps of formingthe CSMAE bilayer and annealing the CSMAE bilayer: forming a protectivelayer atop the CSMAE bilayer to protect its impurity absorbing layer byavoiding its direct contact with an annealing environment.
 14. Themethod of claim 13 wherein the protective layer comprises a materialselected from a group consisting of: Cu, Ru, Al, Rh, Ag, and Au.
 15. Themethod of claim 1 wherein etching out a top portion of the device inprocess comprises: performing one or more etching processes.
 16. Themethod of claim 15 wherein the etching process comprises one or more of:a reactive ion etching (RIE) process, preferably using one or more ofCH3OH gas chemistry and a mixture of NH3 and CO gas chemistry; and anion bean etching (IBE) process.
 17. The method of claim 1 furthercomprises, after the step of etching out a top portion of the device inprocess: forming an upper contact layer, comprising a buffer layer and aphotoresist layer, above a remaining CS MAE bilayer.
 18. The method ofclaim 1 further comprises, when necessary after the step of etching outa top portion of the device in process, oxidizing a top surface of aremaining CSMAE bilayer for forming a thin film having an interfacialthermal stability and a function as a diffusion barrier, using anoxidizing agent, preferably comprising Argon and a gas selected from agroup consisting of: natural oxygen, radical oxygen, and ionized oxygen.19. The method of claim 1 wherein forming the reference layer comprisesone or more of forming a magnetic anisotropy and invariablemagnetization in a direction perpendicular to a film surface of thereference layer; and forming a magnetic anisotropy and invariablemagnetization in a direction parallel to a film surface of the referencelayer.
 20. The method of claim 1 wherein forming the recording layercomprises one or more of forming a magnetic anisotropy and variablemagnetization in a direction perpendicular to a film surface of thereference layer; and forming a magnetic anisotropy and variablemagnetization in a direction parallel to a film surface of the referencelayer.